base 9 is a positional numeral system with nine as its base. It uses 9 different digits for representing numbers. The digits for base 9 could be 0, 1, 2, 3, 4, 5, 6, 7, and 8.

conversion table

base 9	base 7	base 9	base 7
1	≈ 1	12	≈ 14
2	≈ 2	13	≈ 15
3	≈ 3	14	≈ 16
4	≈ 4	15	≈ 20
5	≈ 5	16	≈ 21
6	≈ 6	17	≈ 22
7	≈ 10	18	≈ 23
8	≈ 11	20	≈ 24
10	≈ 12	21	≈ 25
11	≈ 13	22	≈ 26